Utilizing the unique genetic flexibility of the fruit fly, Drosophila melanogaster, we intend to probe by means of genetic analysis and the technology of molecular biology the function and structure of several redundant genes in this organism. Specifically, will be concerned with the ribosomal RNA genes (rDNA), the 5S RNA genes (5S DNA) and the tRNA genes (tDNA). Our proposed research can be divided into three major aspects. First, we intend to search for mutations that regulate the expression of the 5S DNA. These experiments involve mutagenesis, genetic analysis and biochemical and genetic characterization of 5S DNA mutants. Second, by physical means we intend to measure the length of structural gene and spacer sequence for rDNA, 5S DNA and tDNA. We also intend to determine if the size of the rDNA spacer region is altered after several alternating rDNA magnification and reduction events. In addition, we shall determine if the isoaccepting tRNA genes are clustered. Third, by employment of nucleic acid hybridization techniques and analysis by restriction enzymes, we are in the process of developing a methodology for analyzing the spacer DNA sequences extending from the 3'-OH end of any RNA transcript. These structural studies should provide some insight as to the functional significance of spacer DNA in the eukaryotic genome.